Career
Sau has been nicknamed Pattolino (Duckling) since childhood. His idol growing up was the striker Gianfranco Zola, also from his native Province of Nuoro in Sardinia. Foreign three months in 2000, while visiting an uncle in Scotland, he trained at Gourock, the home of the youth team of Livingston F.C.
Cagliari
Sau turned professional at Cagliari in 2007.
On 25 June 2008 he was signed by AlbinoLeffe.
On 15 July 2009, he was loaned to Lecco. Foggia
In August 2010 Sau was acquired by Foggia of Lega Pro Prima Divisione by head coach Zdenek Zeman in co-ownership deals, for a peppercorn of €500, scoring 20 league goals that season.
In June 2011 Foggia acquired Sau and Salvatore Burrai outright for a total of €207,000 by a closed tender mediated by Lega Serie A. However they were returned to Cagliari on 31 August 2011 for the same total price (Burrai for free and Sau for €207,000). Foggia later brought the transfer to court to claim the transfer documents were falsified.
Foggia went bankrupted in 2012.
Return to Cagliari
Sau was re-acquired by Cagliari on 31 August 2011 in a 2-year contract. He played at South.S. Juve Stabia in 2011-2012 Serie B season, scoring 21. This form allowed him into the Cagliari first team for 2012-2013.
Sau scored both of Cagliari"s goals in a 2–2 draw against Inter on 18 November 2012.
On 29 August 2014 Sau renewed his contract with Cagliari again.